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VOP_LOOKUP(9)	       FreeBSD Kernel Developer's Manual	 VOP_LOOKUP(9)

NAME
     VOP_LOOKUP	-- lookup a component of a pathname

SYNOPSIS
     #include <sys/vnode.h>
     #include <sys/namei.h>

     int
     VOP_LOOKUP(struct vnode *dvp, struct vnode	**vpp,
	 struct	componentname *cnp);

DESCRIPTION
     This VFS entry point looks	up a single pathname component in a given
     directory.

     Its arguments are:

     dvp  the locked vnode of the directory to search

     vpp  the address of a variable where the resulting	locked vnode should be
	  stored

     cnp  the pathname component to be searched	for

     Cnp is a pointer to a componentname structure defined as follows:

     struct componentname {
	     /*
	      *	Arguments to lookup.
	      */
	     u_long  cn_nameiop;     /*	namei operation	*/
	     u_long  cn_flags;	     /*	flags to namei */
	     struct  proc *cn_proc;  /*	process	requesting lookup */
	     struct  ucred *cn_cred; /*	credentials */
	     /*
	      *	Shared between lookup and commit routines.
	      */
	     char    *cn_pnbuf;	     /*	pathname buffer	*/
	     char    *cn_nameptr;    /*	pointer	to looked up name */
	     long    cn_namelen;     /*	length of looked up component */
	     u_long  cn_hash;	     /*	hash value of looked up	name */
	     long    cn_consume;     /*	chars to consume in lookup() */
     };

     Convert a component of a pathname into a pointer to a locked vnode.  This
     is	a very central and rather complicated routine.	If the file system is
     not maintained in a strict	tree hierarchy,	this can result	in a deadlock
     situation.

     The cnp-_cn_nameiop argument is LOOKUP, CREATE, RENAME, or	DELETE depend-
     ing on the	intended use of	the object.  When CREATE, RENAME, or DELETE is
     specified,	information usable in creating,	renaming, or deleting a	direc-
     tory entry	may be calculated.

     Overall outline of	VOP_LOOKUP:

	   Check accessibility of directory.   Look  for  name	in  cache,  if
	   found,  then	 return	 name.	 Search	for name in directory, goto to
	   found or notfound as	appropriate.

     notfound:

	   If creating or renaming and at end of pathname, return EJUSTRETURN,
	   leaving info	on available slots else	return ENOENT.

     found:

	   If at end of	path and deleting, return information to allow delete.
	   If at end of	path and renaming, lock	target inode and  return  info
	   to  allow  rename.  If not at end, add name to cache; if at end and
	   neither creating nor	deleting, add name to cache.

LOCKS
     The directory, dvp	should be locked on entry.  If an error	(note: the
     return value EJUSTRETURN is not considered	an error) is detected, it will
     be	returned locked.  Otherwise, it	will be	unlocked unless	both
     LOCKPARENT	and ISLASTCN are specified in cnp-_cn_flags.  If an entry is
     found in the directory, it	will be	returned locked.

RETURN VALUES
     Zero is returned with *vpp	set to the locked vnode	of the file if the
     component is found.  If the component being searched for is ".", then the
     vnode just	has an extra reference added to	it with	vref(9).  The caller
     must take care to release the locks appropriately in this case.

     If	the component is not found and the operation is	CREATE or RENAME, the
     flag ISLASTCN is specified	and the	operation would	succeed, the special
     return value EJUSTRETURN is returned.  Otherwise, an appropriate error
     code is returned.

PSEUDOCODE
     int
     vop_lookup(struct vnode *dvp,
		struct vnode **vpp,
		struct componentname *cnp)
     {
	 int error;
	 int nameiop = cnp->cn_nameiop;
	 int flags = cnp->cn_flags;
	 int lockparent	= flags	& LOCKPARENT;
	 int islastcn =	flags &	ISLASTCN;
	 struct	vnode *vp = NULL;

	 /*
	  * Check accessibility	of directory.
	  */
	 if (dvp->v_type != VDIR)
	     return ENOTDIR;

	 error = VOP_ACCESS(dvp, VEXEC,	cred, cnp->cn_proc);
	 if (error)
	     return (error);

	 if (islastcn && (dvp->v_mount->mnt_flag & MNT_RDONLY) &&
	     (cnp->cn_nameiop == DELETE	|| cnp->cn_nameiop == RENAME))
	     return (EROFS);

	 /*
	  * Check name cache for directory/name	pair.  This returns ENOENT
	  * if the name	is known not to	exist, -1 if the name was found, or
	  * zero if not.
	  */
	 error = cache_lookup(dvp, vpp,	cnp);
	 if (error) {
	     int vpid;

	     if	(error = ENOENT)
		 return	error;

	     vp	= *vpp;
	     if	(dvp ==	vp) {	     /*	lookup on "." */
		 VREF(vp);
		 error = 0;
	     } else if (flags &	ISDOTDOT) {
		 /*
		  * We need to unlock the directory before getting
		  * the	locked vnode for ".." to avoid deadlocks.
		  */
		 VOP_UNLOCK(dvp);
		 error = vget(vp, 1);
		 if (!error) {
		     if	(lockparent && islastcn)
			 error = VOP_LOCK(dvp);
		 }
	     } else {
		 error = vget(vp, 1);
		 if (error || !(lockparent && islastcn)) {
		     VOP_UNLOCK(dvp);
		 }
	     }

	     /*
	      *	Check that the capability number did not change
	      *	while we were waiting for the lock.
	      */
	     if	(!error) {
		 if (vpid == vp->v_id) {
		     /*
		      *	dvp is locked if lockparent && islastcn.
		      *	vp is locked.
		      */
		     return (0);
		 }
		 vput(vp);

		 if (dvp != vp && lockparent &&	islastcn)
		     VOP_UNLOCK(pdp);
	     }

	     /*
	      *	Re-lock	dvp for	the directory search below.
	      */
	     error = VOP_LOCK(dvp);
	     if	(error)	{
		 return	(error);
	     }

	     *vpp = NULL;
	 }

	 /*
	  * Search dvp for the component cnp->cn_nameptr.
	  */
	 ...;

	 if (!found) {
	     if	((nameiop == CREATE || nameiop == RENAME)
		 && islastcn
		 && directory dvp has not been removed)	{
		 /*
		  * Check for write access on directory.
		  */

		 /*
		  * Possibly record the	position of a slot in the directory
		  * large enough for the new component name.  This can be
		  * recorded in	the vnode private data for dvp.
		  * Set	the SAVENAME flag to hold onto the pathname for	use
		  * later in VOP_CREATE	or VOP_RENAME.
		  */
		 cnp->cn_flags |= SAVENAME;
		 if (!lockparent)
		     /*
		      *	Note that the extra data recorded above	is only
		      *	useful if lockparent is	specified.
		      */
		     VOP_UNLOCK(dvp);

		 return	EJUSTRETURN;
	     }

	     /*
	      *	Consider inserting name	into cache.
	      */
	     if	((cnp->cn_flags	& MAKEENTRY) &&	nameiop	!= CREATE)
		 cache_enter(dvp, NULL,	cnp);

	     return ENOENT;
	 } else	{
	     /*
	      *	If deleting, and at end	of pathname, return parameters
	      *	which can be used to remove file.  If the wantparent flag
	      *	isn't set, we return only the directory, otherwise we go on
	      *	and lock the inode, being careful with ".".
	      */
	     if	(nameiop == DELETE && islastcn)	{
		 /*
		  * Check for write access on directory.
		  */
		 error = VOP_ACCESS(dvp, VWRITE, cred, cnp->cn_proc);
		 if (error)
		     return (error);

		 if (found entry is same as dvp) {
		     VREF(dvp);
		     *vpp = dvp;
		     return 0;
		 }

		 error = VFS_VGET(dvp->v_mount,	..., &vp);
		 if (error)
		     return error;

		 if (directory is sticky
		     &&	cred->cr_uid !=	0
		     &&	cred->cr_uid !=	owner of dvp
		     &&	owner of vp != cred->cr_uid) {
		     vput(vp);
		     return EPERM;
		 }
		 *vpp =	vp;
		 if (!lockparent)
		     VOP_UNLOCK(dvp);

		 return	0;
	     }

	     /*
	      *	If rewriting (RENAME), return the inode	and the
	      *	information required to	rewrite	the present directory
	      *	Must get inode of directory entry to verify it's a
	      *	regular	file, or empty directory.
	      */
	     if	(nameiop == RENAME && wantparent && islastcn) {
		 error = VOP_ACCESS(dvp, VWRITE, cred, cnp->cn_proc);
		 if (error)
		     return (error);

		 /*
		  * Check for "."
		  */
		 if (found entry is same as dvp)
		     return EISDIR;

		 error = VFS_VGET(dvp->v_mount,	..., &vp);
		 if (error)
		     return error;
		 *vpp =	vp;
		 /*
		  * Save the name for use in VOP_RENAME	later.
		  */
		 cnp->cn_flags |= SAVENAME;
		 if (!lockparent)
		     VOP_UNLOCK(dvp);

		 return	0;
	     }

	     /*
	      *	Step through the translation in	the name.  We do not `vput' the
	      *	directory because we may need it again if a symbolic link
	      *	is relative to the current directory.  Instead we save it
	      *	unlocked as "pdp".  We must get	the target inode before	unlocking
	      *	the directory to insure	that the inode will not	be removed
	      *	before we get it.  We prevent deadlock by always fetching
	      *	inodes from the	root, moving down the directory	tree. Thus
	      *	when following backward	pointers ".." we must unlock the
	      *	parent directory before	getting	the requested directory.
	      *	There is a potential race condition here if both the current
	      *	and parent directories are removed before the VFS_VGET for the
	      *	inode associated with ".." returns.  We	hope that this occurs
	      *	infrequently since we cannot avoid this	race condition without
	      *	implementing a sophisticated deadlock detection	algorithm.
	      *	Note also that this simple deadlock detection scheme will not
	      *	work if	the file system	has any	hard links other than ".."
	      *	that point backwards in	the directory structure.
	      */
	     if	(flags & ISDOTDOT) {
		 VOP_UNLOCK(dvp);    /*	race to	get the	inode */
		 error = VFS_VGET(dvp->v_mount,	..., &vp);
		 if (error) {
		     VOP_LOCK(dvp);
		     return (error);
		 }
		 if (lockparent	&& islastcn) {
		     error = VOP_LOCK(dvp);
		     if	(error)	{
			 vput(vp);
			 return	error;
		     }
		 }
		 *vpp =	vp;
	     } else if (found entry is same as dvp) {
		 VREF(dvp);  /*	we want	ourself, ie "."	*/
		 *vpp =	dvp;
	     } else {
		 error = VFS_VGET(dvp->v_mount,	..., &vp);
		 if (error)
		     return (error);
		 if (!lockparent || !islastcn)
		     VOP_UNLOCK(dvp);
		 *vpp =	vp;
	     }

	     /*
	      *	Insert name into cache if appropriate.
	      */
	     if	(cnp->cn_flags & MAKEENTRY)
		 cache_enter(dvp, *vpp,	cnp);
	     return (0);
	 }
     }

ERRORS
     [ENOTDIR]		The vnode dvp does not represent a directory.

     [ENOENT]		The component dvp was not found	in this	directory.

     [EACCESS]		access for the specified operation is denied.

     [EJUSTRETURN]	a CREATE or RENAME operation would be successful

SEE ALSO
     VOP_ACCESS(9), VOP_CREATE(9), VOP_MKNOD(9), VOP_MKDIR(9), VOP_SYMLINK(9),
     VOP_RENAME(9), VOP_ABORTOP(9)

HISTORY
     The function VOP_LOOKUP appeared in 4.3BSD.

SEE ALSO
     vnode(9)

AUTHORS
     This man page was written by Doug Rabson, with some text from comments in
     ufs_lookup.c.

FreeBSD				 July 24, 1996			       FreeBSD

NAME | SYNOPSIS | DESCRIPTION | LOCKS | RETURN VALUES | PSEUDOCODE | ERRORS | SEE ALSO | HISTORY | SEE ALSO | AUTHORS

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